Field of the Invention
The present invention relates to a hydraulic drive system.
Background Information
Work machines such as a hydraulic excavator or a wheel loader are equipped with working instrument driven by a hydraulic cylinder. Hydraulic fluid discharged from a hydraulic pump is supplied to the hydraulic cylinder. The hydraulic fluid is supplied via a hydraulic circuit to the hydraulic cylinder. For example, Japan Patent Laid-open Patent Publication JP-A-2009-511831 describes a work machine equipped with a hydraulic closed circuit for supplying hydraulic fluid to the hydraulic cylinder. Potential energy of the working instrument is regenerated due to the hydraulic circuit being a closed circuit. As a result, fuel consumption of a motor for driving the hydraulic pump can be reduced.